It is noticeable that the coalition of the willing includes mostly Common Law countries such as the UK, USA and Australia while many Civil Law jurisdictions such as France and Germany were hostile to Operation Iraqi Freedom. It is possible to make too much of this: Ireland and Canada are both Common Law states while most of continental Europe (which is entirely Civil Law) backed the coalition, but there is a small trend at work here.
Plainly, Iraqi liberation is covered by the Common Law doctrine of self-defence, which can be pre-emptive and, oddly, can involve defending others. That Saddam was, on an ongoing basis, involved in crimes against humanity is self-evident. It is also clear that the response was proportionate, since Saddam has been removed by less violence than he was inflicting. The same is true for regime change in Afghanistan.
Recent assertive American foreign policies failed this test during the Clinton era. Bombing from 7,500 feet - at least where it is the sole response - can almost never be self-defence. Boots on the ground are necessary for the response to be proportionate.
To take an individual example, if I see someone pointing a gun at you, I can shoot that person. The response is proportionate, and therefore covered by self-defence. What I cannot do is drop a bomb on that person killing everyone in a three block radius because a) that is not proportionate and b) it doesn't defend anyone, the victim is also killed.
Clinton's overriding fear of exposing American volunteer soldiers to danger led to some pretty foul calculations - eg, one American life is equivalent to 85,000 Rwandans - but it also led to illegal actions.
Clare Short and the late (and therefore canonised) Robin Cook were eager to support regime change in Serbia and Operation Desert Fox in Iraq, which were, under Common Law, illegal as well as being immoral. They would not support the perfectly legal and highly moral Operation Iraqi Freedom. What does this say about them?